This is a new project. Methods have been developed to successfully transplant skin from humans, rats and mice onto athymic nude mice. Human skin has been transplanted from patients with and without xeroderma pigmentosa. The acute morphological effects of ultraviolet light, N-methyl-N'-nitro-N-nitroso-guanidine, 7,12-dimethylbenz(a)anthracene and 12-0-tetradecanoyl phorbol- 13-acetate have been determined. Based on these results chronic experiments are in progress.